1. Field of the Invention
The present invention relates to a cylindrical grinding machine for grinding a workpiece supported rotatably about an axis, with a grinding wheel which is movable in a lengthwise direction of the workpiece as well as in a direction across thereto. More particularly, it relates to a cylindrical grinding machine particularly designed for efficient discharge of coolant from a machining area to the outside of the grinding machine.
2. Discussion of the Related Art
Cylindrical grinding machines of this kind are of the type that a grinding wheel is movable in a lengthwise direction of a workpiece as well as in a direction across thereto and are known as so called “wheel head traverse type grinding machine”. The Japanese unexamined, published patent application No. 2002-292546 discloses one example of the wheel head traverse type grinding machine. In this known grinding machine, a work head and a foot stock collectively referred to as work support device on a bed sustains opposite ends of the workpiece to enable the same to rotate about one axis. Further, on the bed, traverse guide ways parallel to the axis are provided directly on the bed or on a fixed base secured on the bed and a movable base is movably guided along the guide ways. A wheel head rotatably carrying a grinding wheel is mounted on the movable base to be movable back and forth in a direction perpendicular to the traverse guide ways. The wheel head is moved bodily with the movable base in the longitudinal or lengthwise direction and is moved to and from the workpiece on the movable base.
The portion on the bed which is under a machining area including a grinding point where the grind wheel comes into contact with the workpiece is formed as a coolant collecting portion, toward which grinding fluid or coolant ejected to the machining area falls down. The coolant collected by the coolant collecting portion flows along a slanted path on the bed and is returned to a coolant supply device from an outlet opening to the upper surface of the bed. Conventionally, the coolant supply device is arranged separated from the body of the grinding machine to be placed by the lateral portion of the bed. A reservoir section of the coolant supply device is connected through a plastic or vinyl pipe to the outlet to receive the coolant which is discharged from the upper surface of the bed through the outlet to the outside of the machine.
Further, since grinding chips are liable to be deposited on the coolant collecting portion on the bed which is under the machining area, measures are usually taken that coolant is flown all the time on the upper surface of the bed thereby to actively feed the grinding chips toward the outlet. Especially, in a grinding method wherein coolant used therein is restrained in volume to ten percents or less of that used in a traditional grinding method, coolant hardly rushes on the bed and hence, grinding chips are apt to be deposited on the portion of the bed under the machining area. To remove the deposited grinding chips, the measures are taken to make the flow of coolant all the time on the upper surface on the bed.
However, in the aforementioned known cylindrical grinding machine of the wheel head traverse type, most of the coolant supplied to the machining area falls down directly on the coolant collecting portion under the machining area on the upper surface of the bed, which gives rise to a drawback that a thermally adverse influence is exerted on the bed. In particular, where coolant flow is made for discharging grinding chips, thermally adverse influence comes into existence notably as the thermal deformation of the bed and hence, as a dispersion in size of machined workpieces.
In addition, the coolant having fallen down on the coolant collecting portion remains on the bed in a substantial volume until it is flown together with the grinding chip discharge coolant back to the reservoir of the coolant supply device. This makes it unavoidable to use a coolant supply device needing a large volume of coolant, in which case the volume of coolant remaining on the bed for a time lag in collection has to be taken into consideration. As a result, a large burden is imposed not only on the maintenance of the coolant in use but also on the disposal of a large volume dirty coolant having expired its life in use.
Furthermore, most of the coolant having supplied to around the grinding point is collected to the coolant supply device through a predetermined discharge path arranged on the grinding machine, whereas a part of the coolant scatters to make mist staying in the machining area. To this end, in prior art grinding machines, it has been customary that a cover device is provided to surround the machining area and that a mist collection device is arranged to collect mist from the space surrounded by the cover device. On the other hand, most of the coolant falls down onto a portion of the bed under the machining area and is then collected to the coolant supply device through the discharge path formed on the upper surface of the bed. For this reason, there have been needed two systems: a discharge path for collecting the coolant in the form of fluid and a mist collecting path for collecting mist. This disadvantageously results in making the collecting mechanisms for coolant and mist complicated in construction as well as in needing separate maintenance works therefor.
In order to solve the aforementioned problem, in a coolant collecting apparatus for a grinding machine disclosed in Japanese unexamined, published patent application No. 5-16072, a collecting path for the coolant which falls down right under a machining area where a grinding wheel acts on a workpiece is constituted in the form of a duct passing through a bed, and the inside of the duct is exhausted by a mist collecting apparatus. Thus, through the duct, coolant and mist are discharged outside the grinding machine, and the coolant is directly collected by the coolant collecting apparatus, while the mist is sucked by the mist collecting device.
However, in the foregoing coolant collecting apparatus, the mist collecting device not only has a suction inlet which opens to the duct formed in the bed of the grinding machine but also has another suction inlet which opens to a coolant reservoir constituting the coolant collecting device to be spaced apart from the upper surface of the coolant contained in the reservoir. That is, the mist collecting device collects not only the mist passing through the duct but also the mist which is filled up in the reservoir by being atomized when collected into the reservoir. Thus, the capability of the mist collecting device for collecting the mist from the duct, namely from the machining area is reduced by collecting the mist from the reservoir, whereby there occurs a problem that the mist suspended in the machining area cannot be collected effectively or efficiently.